The highways department are only concerned about safety of vehicles coming in and going out. Hence, they have no concern over that which is why they have not objected. The council on the other hand whilst they will consider those safety issues are concerned about the removal of trees and the general effect on the local environment.
As I said earlier, there is no absolute right to vehicle access from Highway.
What you can do apart from the usual appeal and exchange of correspondence is tell them that if they steadfastly refuse this, you will have to consider making an application for judicial review.
Judicial review will be expensive if you lose but then again, it will also be expensive if they lose. Local authorities do not like defending applications for judicial review. You can only bring an application for judicial review on the basis that the decision of the Council was illegal irrational or had not complied with the character procedure for dealing with this there are no the grounds.
Even if you are successful and you get the judicial review order, it will not necessarily change the decision. It just makes the local authority revisit the way and the reasons behind the decision. The decision may remain the same.
It appears here that the decision is irrational because all the objections they have put forward don’t seem to hold water.
If you do not have the money to risk the judicial review, (you are potentially looking at a legal bill of £10,000 oto be paid by the user to the winner), then apart from arguing the toss and appealing the decision, you can make a formal complaint to the Local Government Ombudsman which fortunately is free.
Can I clarify anything for you?
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